/*
silverPDF is sponsored by Aleyant Systems (http://www.aleyant.com)

silverPDF is based on PdfSharp (http://www.pdfsharp.net) and iTextSharp (http://itextsharp.sourceforge.net)

Developers: Ai_boy (aka Oleksii Okhrymenko)

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above information and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR SPONSORS
BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

*/
#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   David Stephensen (mailto:David.Stephensen@pdfsharp.com)
//
// Copyright (c) 2005-2008 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

using System;
using System.Diagnostics;
using System.Text;
using System.IO;

namespace PdfSharp.Pdf.Filters
{
  /// <summary>
  /// Implements the LzwDecode filter.
  /// </summary>
  public class LzwDecode : Filter
  {
    /// <summary>
    /// Throws a NotImplementedException because the obsolete LZW encoding is not supported by PDFsharp.
    /// </summary>
    public override byte[] Encode(byte[] data)
    {
      throw new NotImplementedException("PDFsharp does not support LZW encoding.");
    }

    /// <summary>
    /// Decodes the specified data.
    /// </summary>
    public override byte[] Decode(byte[] data, FilterParms parms)
    {
      if (data[0] == (byte)0x00 && data[1] == (byte)0x01)
        throw new Exception("LZW flavour not supported.");

      MemoryStream outputStream = new MemoryStream();

      InitializeDictionary();

      this.data = data;

      bytePointer = 0;

      nextData = 0;
      nextBits = 0;

      int code, oldCode = 0;
      byte[] str;

      while ((code = this.NextCode) != 257)
      {
        if (code == 256)
        {
          InitializeDictionary();
          code = NextCode;
          if (code == 257)
          {
            break;
          }
          outputStream.Write(stringTable[code], 0, stringTable[code].Length);
          oldCode = code;

        }
        else
        {
          if (code < tableIndex)
          {
            str = stringTable[code];
            outputStream.Write(str, 0, str.Length);
            AddEntry(stringTable[oldCode], str[0]);
            oldCode = code;
          }
          else
          {
            str = stringTable[oldCode];
            outputStream.Write(str, 0, str.Length);
            AddEntry(str, str[0]);
            oldCode = code;
          }
        }
      }

      if (outputStream.Length >= 0)
      {
        outputStream.Capacity = (int)outputStream.Length;
        return outputStream.GetBuffer();
      }
      return null;
    }

    /// <summary>
    /// Initialize the dictionary.
    /// </summary>
    void InitializeDictionary()
    {
      stringTable = new byte[8192][];

      for (int i = 0; i < 256; i++)
      {
        stringTable[i] = new byte[1];
        stringTable[i][0] = (byte)i;
      }

      tableIndex = 258;
      bitsToGet = 9;
    }

    /// <summary>
    /// Add a new entry to the Dictionary.
    /// </summary>
    void AddEntry(byte[] oldstring, byte newstring)
    {
      int length = oldstring.Length;
      byte[] str = new byte[length + 1];
      Array.Copy(oldstring, 0, str, 0, length);
      str[length] = newstring;

      stringTable[tableIndex++] = str;

      if (tableIndex == 511)
        bitsToGet = 10;
      else if (tableIndex == 1023)
        bitsToGet = 11;
      else if (tableIndex == 2047)
        bitsToGet = 12;
    }

    /// <summary>
    /// Returns the next set of bits.
    /// </summary>
    int NextCode
    {
      get
      {
        try
        {
          nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
          nextBits += 8;

          if (nextBits < bitsToGet)
          {
            nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
            nextBits += 8;
          }

          int code = (nextData >> (nextBits - bitsToGet)) & andTable[bitsToGet - 9];
          nextBits -= bitsToGet;

          return code;
        }
        catch
        {
          return 257;
        }
      }
    }

    int[] andTable = { 511, 1023, 2047, 4095 };
    byte[][] stringTable;
    byte[] data = null;
    int tableIndex, bitsToGet = 9;
    int bytePointer;
    int nextData = 0;
    int nextBits = 0;
  }
}
